A double sextant, 1797.

Double sextant. © National Maritime Museum, London

Repro ID: D6085

Description: The sextant takes its name from its shape, a sixth of a circle. Astronomical sextants had been in use since the 16th century but the marine version was developed in about 1757 by Captain John Campbell, with the help of the London instrument maker John Bird. It worked on exactly the same principle as the octant but, having a longer scale, could be used for angles up to 120 degrees. This example has the double frame patented by Edward Troughton in 1788, which provided rigidity without too much weight. It was given as a presentation piece and bears the inscription, 'The Gift of Capt Jas Brisbane to Mr. T.H. Hoskins Master of HM Ship 'Saturn' 1802'.

Creator: John and Edward Troughton

Date: 1797

Credit line: National Maritime Museum, London